Generally, concrete fabricated by using portland cement has alkalinity, and is very susceptible to acidity. This concrete is mainly degraded by a chemical reaction. The most representative degradation of the concrete is corrosion due to salt damage or neutralization. Especially, a concrete structure exposed to salt damage environments may be early degraded due to corrosion of reinforced steel. Works to prevent the degradation of the concrete structure and to reinforce the concrete structure are generally performed by laminating epoxy or reinforcing glass mat to each other. This may cause operating time and material costs to be increased.
In order to solve the weak chemical resistance and strength of the concrete, has been developed a modified sulfur concrete technique capable of using modified sulfur materials rather than portland cement as a binder, and capable of fabricating mortar or concrete by mixing the modified sulfur binder with each kind of aggregate. In the case of using the modified sulfur binder, water is not used due to characteristics of the modified sulfur concrete, but a melted material obtained by melting modified sulfur is used.
However, the modified sulfur concrete has limited applicable ranges due to underwater freezing and thawing resistance, surface concavity due to a temperature difference between inside and outside of a test piece due to a rapid cooling after pouring, preheating of aggregate or a mould, susceptibility to fire, etc.
According to the current techniques, the modified sulfur concrete has to be used under the earth, under the sea, and under water. These limited applicable ranges may cause the modified sulfur concrete not to be universally used as materials for construction.
More concretely, have been continuously developed techniques for applying sulfur to civil engineering works and construction fields, by using characteristics of the sulfur having a melting point of 119° C. and having a solid phase at a room temperature. For instance, the sulfur is considered to be used as a binder such as packaging materials (U.S. Pat. No. 4,290,816), construction materials (Japanese Patent Publication No. 55-49024), or waste solidification materials (Japanese Patent Publication No. 62-15274), etc. With respect to combustibility, the sulfur has a flash point of 207° C. and a spontaneous combustion temperature of 245° C. Accordingly, the sulfur has an ignition quality, and may be easily burned when exposed to outside. With respect to a mechanical strength, the sulfur has a high strength when there is no defection in a stable solid state.
However, when solidified by cooling from a liquid state, the sulfur is in a mixed state among three types of an orthorhombic system, a monoclinic crystal, and amorphous sulfur. And, the sulfur has a mixing ratio changed according to cooling conditions, and has defections or brittleness as time lapses. This may result in very limited applicable ranges of the sulfur in the case of using pure sulfur as a binder. In order to solve the problems, various types of sulfur modifiers have been researched.
Especially, dicyclopentadiene (DCPD) is cheap, and has a good mechanical strength as disclosed in New Uses of Sulfur-11, 1978, PP. 68-77, 1978.
Japanese Patent Publication Nos. 2-25929 and 2-28529 have disclosed a method capable of improving properties and shapes of sulfur by adding vinyl toluene, dipentene, and olefin oligomer to the sulfur, and utilizing the sulfur as packaging materials, adhering materials, waterproofing materials, etc.
Japanese Patent Laid-Open No. 2003-277108 has disclosed tetra hydraulic indene as a sulfur modifier. And, Japanese Patent Laid-Open No. 2002-60491 has disclosed dicyclopentadiene and tetra hydraulic indene as a sulfur modifier. Actually, mixed materials between asphalt and sulfur are used as road packaging materials.
Generally, a reaction between dicyclopentadiene and sulfur may be considered as a polymerization reaction, and a relevant reaction mechanism has been disclosed in U.S. Pat. No. 4,311,826. In order to fabricate modified sulfur, dicyclopentadiene and sulfur are chemically reacted at an initial stage, and then the sulfur is changed into high molecular compounds by a radical chain reaction.
However, the continuous reaction between dicyclopentadiene and sulfur results in high heat emission, thereby being controlled with difficulty due to increased temperature and viscosity of the two materials. Furthermore, the dicyclopentadiene and sulfur can not be molded due to drastic solidification at a room temperature.
In order to solve the problems, the U.S. Pat. No. 4,311,826 has disclosed a technique capable of reacting sulfur with 20˜40% by weight of a modifier (a binder of oligomer mixture composed of at least terpolymer of dicyclopentadiene and cyclo pentadiene). Japanese Patent Publication No. 2-28529 and U.S. Pat. No. 4,391,969 disclose a modified sulfur binder, respectively, composed of high polymers obtained by reacting sulfur with 2-20% by weight of a binder (binder containing dicyclopentadiene-oligomer mixture and dicyclopentadiene). Here, at least 37% by weight of cyclo pentadiene oligomer is required to be added to the binder. Korean Patent Laid-Open No. 2006-101878 has disclosed a method for fabricating a modified sulfur binder having an excellent storage stability in a liquid state by controlling less than 2˜4% by weight of additives when exclusively using dicyclopentadiene not containing oligomer more than terpolymer as a binder.
The aforementioned techniques are used to fabricate sulfur concrete or sulfur asphalt by two methods. According to a first method for fabricating sulfur concrete or sulfur asphalt, a modified sulfur binder, a reaction product obtained by melt-mixing dicyclopentadiene and oligomer serving as a binder with sulfur at 120˜160° C., is cooled at a room temperature less than 120° C. to be solidified, and then the modified sulfur binder is re-melted in a specific mixer having a temperature of 120-160° C. Then, the preheated aggregate and additives are simultaneously mixed with the modified sulfur binder as soon as possible, and the mixture is introduced into a preheated mould (or a molding machine) thus to be solidified by cooling.
According to a second method for fabricating sulfur concrete or sulfur asphalt, sulfur, a binder, and aggregate is simultaneously melt-mixed in specific conditions, and then the mixture is cooled.
However, the methods for fabricating a modified sulfur binder have the following problems.
Firstly, the modified sulfur binder re-melted to be mixed with aggregate for fabrication of concrete continuously undergoes a polymerization process even at 120-160° C., thereby having an increased viscosity. This may cause the fabrication processes not to be smoothly performed.
Secondly, when melt-mixing time of the modified sulfur binder in the mixer is too short, the modified sulfur binder is not sufficiently mixed with the aggregate. This may cause the resulting mixture to have holes or a rough surface in a non-consecutive manner.
Thirdly, when a melted mixture has a lowered temperature, the fluidity is degraded and the operation is not smoothly performed. This may cause drastic solidification of the melted mixture by cooling. In order to prevent this problem, the melt-mixing time has to be short within an allowance range of a physical property of fabricated sulfur concrete.
According to the conventional method, sulfur and dicyclopentadiene are reacted with each other to fabricate a modified sulfur binder in a solid phase, and then the modified sulfur binder is mixed with aggregate to fabricate concrete, etc.
All the fabricated modified sulfur binders, or materials for civil engineering and construction containing the modified sulfur binders have cheaper fabrication costs than cement, and have excellent physical properties such as high strength, high chemical resistance, and a hardened characteristic at a high speed. However, all the fabricated modified sulfur binders or materials have to be used under the earth, under the sea, and under water due to susceptibility to fire. These limited applicable ranges may cause the modified sulfur binders not to be universally used as materials for construction.
Japanese Patent Laid-Open Nos. 2003-277108 and 2004-2113 have disclosed modified sulfur concrete having more excellent stability than pure sulfur concrete as a test result of fire retardancy or ignition quality. However, the modified sulfur concrete corresponding to polymer concrete is ignited within a short time when contacting a large heat source such as fire, thus to lost functions as a concrete structure. This may cause large catastrophes such as earthquake to consecutively occur.